Japan's Meteorological Agency issued and then canceled warnings on the main northern island, Hokkaido, though advisories remained for Pacific coast towns elsewhere, from northern Aomori to Wakayama in the west.

The agency said the quake struck around 1:24 p.m. (0424 GMT) near the Kuril Trench, about 500 kilometers (310 miles) east of Etorofu, one of four disputed island groups called the Northern Territories in Japan and the Kuril islands in Russia.

It was 30 kilometers (19 miles) below the seabed, the agency said.

More than three hours after the quake, the largest wave, at 40 centimeters (16 inches), twice hit Chichi-jima, an island of 2,000 people about 1,000 kilometers (620 miles) south of Tokyo.

Small tidal swells were observed elsewhere, the agency said.

No injuries or damage were immediately reported from the offshore quake, said Hokkaido prefectural police spokesman Shinji Yamakoshi.

He said he did not feel the quake at his headquarters in the island's western city of Sapporo.

A tsunami warning was also issued for Alaska's western Aleutian islands, prompting some residents to flee. A tsunami watch issued for Hawaii was later canceled.

In Japan, Hokkaido disaster prevention official Haruyuki Komachi said earlier that 85,000 people in 22 coastal towns had been ordered to evacuate, and thousands had gathered at community centers.

Officials in one Hokkaido town, Abashiri, requested defense troops to bring the evacuees blankets and other relief goods, and police closed roads to the coast. Some train services were suspended.

The meteorological agency also issued warnings last November following a magnitude 7.9 quake in a similar area, but most areas saw waves of only about 20 centimeters (7.8 inches) high.

In 1993, a quake off western Hokkaido triggered a large tsunami that flattened homes and killed more than 200 people.

The meteorological agency, which then came under fire for insufficient caution, has since begun issuing tsunami warnings even when only tiny waves are expected. Japan's heavily populated coastlines are now fitted with loudspeakers to order tsunami evacuations.

Seismologists, however, warned that Saturday's quake was stronger and cautioned residents to remain vigilant.

Tokyo University seismologist Yoshinobu Tsuji warned that high waves may still hit the region, hours after a tsunami warning.

Citing tidal changes being observed in some locations, Tsuji said "we should assume it's coming ... I urge everyone to stay alert."

Tsunami waves — generated by earthquakes — are often barely noticeable in the ocean but can rise to great heights when they hit shore.

A magnitude 9.1-magnitude earthquake off the coast of Indonesia on Dec. 26, 2004, caused a tsunami that killed more than 230,000 people in 11 countries.